I'm designing a second order DT sigma delta modulator and im using the spectrum assistant to calculate the ENOB.
The values of the circuit are:
so, VREF=1.1V (vcm=900mV)
The circuit is differential and the amplitude of the differential input signal is: 990mV. At the output, im getting the bits stream and im using the spectrum assistant to calculate the parameters. the results are:
ENOB=16.22, SINAD=90.74, and the magnitude of the DFT signal is 810mV.
I'm using the hanning window and i set the peak saturation level to 1.1.
The issue is that i'm comparing the results with the formula of ENOB:
ENOB=(SINAD-1.76+20log((fullscale amplitude)/(Input Amplitude))/6.02
so, i replaced fullscale amplitude=1.1, input amplitude=810mV and SINAD=90.74 and i obtained ENOB=15.24
I only obtained ENOB=16.22 if i calculate like the fullscale amplitud is the double:
ENOB=(SINAD-1.76+20log((2*fullscale amplitude)/(Input Amplitude))/6.02
Can anyone could tell me if i'm not using the rigth formula or it happened before?
PD: I'm using IC615
Thanks in advance